Polymethylene 2-benzothiazolyl carbodithioates



Uited States Patent Ofiice 3,372,150 Patented Mar. 5, 1968 where x is 5 or 6. These compounds are accelerators for the vulcanization of rubber and impart superior processling safety to vulcanizable rubber compositions. The benzothiazolyl group may be substituted, as for example, it may contain a nitro, chloro, lower alkyl, or lower alkoxy group in the benzene ring.

The preparation of the new compounds is described in detail below:

Example 1 A solution was prepared by mixing 6 23 grams (0.55 mole) of heptamethylenimine, 55.7 grams (0.55 mole) of triethyla'm ine, and 200 ml. of ethyl alcohol. To the stirred solution there was then added dropwise, at 5 to 15 C., 41.8 grams 0.55 mole) of carbon disulfide. After stirring for one hour at 25 -30 C., 300 ml. of dimethyl forrnamide was added in one portion, stirring continued for 5 minutes, and 84.8 grams (0.5 mole) of 2-chloro-benzothiazole then added in one portion. The stirred reaction mixture was heated at 80-90 C., for 18 hours, cooled to 30 C, added to 2000 grams of ice water, and stirred at -ll0 C. for one hour. The resulting precipitate was collected by filtration, washed with water until the washings were neutral to litmus, and air-dried at 25 -30 C. After recrystallization from ethyl acetate, the 2 benzothiazolyl hexahydro-l (2 H)-azocine oarbodithioate melted at 104-1 C. The yield was 99% of a light tan solid analyzing 8.36% nitrogen and 29.90% sulfur compared to 8.69% nitrogen and 29.83% sulfur calculated for C15H18N2S3' Example 2 In the procedure of Example 1, an equimolar amount of octamethylenimine was substituted for the heptamethylenimine. The Z-benzothiazolyl octahydro-lH-azo nine-1-carbodithioate was obtained in 99.5% yield as a white solid melting at 153 -l54 C. after recrystallization from ethyl acetate. Analysis gave 8.411% nitrogen and 28.79% sulfu-r compared to 8.32% nitrogen and 28.58% sulfur calculated for C H N S The products of the present invention were tested to determine their effectiveness as rubber vulcanization accelerators. As illustrative of accelerating activity and processing safety in a synthetic rubber stock, butadiene-sty-rene copolymer rubber was blended in a standard formula as follows:

Parts by weight SB-R 1500 100 Carbon black 50 Zinc oxide 4 Stearic acid 2 I Parts by weight Saturated hydrocarbon softener 10 Sulfur 1.75

Tests were carried out employing the compounds on an equimolar basis. To the above there was added in separate stocks accelerator as follows:

Stock Parts by Accelerator Weight A 1. 45 2-benzothlazolyl hexahydrc-1(2H)-azocine carbodithioate. B 1. 51 2-benzothiazolyl octahydro-IH-azonine-lcarbodithloate.

The stocks were cured in the usual manner by heating in a press for various periods of time at 153 C. The physical properties of the optimum cures are recorded:

TABLE I Modulus of Ultimate Stock Elasticity in Tensile at Break Elongation,

lbs/in. at 300% in lbs/in. Percent Elongation The processing safety of the stocks was evaluated by heating in a Mooney plastometer. The time in minutes required for the plasticity to increase 5 points above the 7 minimum was determined. These values are a measure of processing safety, higher times indicating greater process- The Mooney scorch of a similar stock containing as the accelerator 1.33 parts by weight of Z-benzothiazolyl 1- piperidino-carbod-ithioate was 30.4 minutes. The stock containing the 2-benzothiazolyl l-piperidinocar bodithioate developed an ultimate tensile strength of 1500 pounds per square inch at optimum cure under the same conditions.

Ethylene-propylene terpolymer is the well-recognized and commonly employed name applied to the polymerized rubbery product from polymerization of ethylene, propylene, and a small quantity of a non-coniugated 'diene. To demonstrate the effectiveness of the compounds of this invention as accelerators for the vulcanization of terpolymers, base formulations were prepared comprising:

Parts by weight Ethylene-propylene terpolymer 100 Zinc oxide 5 Carbon black Aromatic processing oil 40 Sulfur 1.5 Thiuram monosulfide 1 Stock:

C 2-benzothiazolyl hexahydro-l(2H)-azocinecarbodithioate D 2 benzothiazolyl octahydro-lH-azonine-lcarbodithioate The stocks so compounded were cured in the usual manner by heating in a press at 160 C. The modulus and tensile properties of the vulcanizates at optimum cure and resistance of the unvulcanized compositions to scorch are set forth below:

TABLE III Modulus of Elasticity in Tensile at Ultimate Mooney Stock lbs/in. at Break in Elo11g., Scorch Mins.

300% Elongalbs/in. Percent at 135 tion The foregoing data show that the compounds of this invention are useful as accelerators and impart greater processing safety as compared to the known Z-benzothiazolyl l-piperidinocarbodithioate.

Rubber in which the products of the present invention are useful as accelerators include both natural rubber and synthetic rubber. The rubber is preferably a diene polymer rubber by which is meant a rubber containing sufficient diene to render it sulfur vulcanizable. Hydrocarbon diene rubbers are preferred, but also useful are copolymers of diene hydrocarbons and acrylonitrile. Further examples of suitable rubbers are isobutylene copolymerized with a small amount of conjugated diene (butyl rubber), cis-1,4-polyisoprene, and cis-1,4-polybutadiene. In general, the amount of accelerator will fall within the range of 0.1 to 5.0 parts by weight per 100 parts by weight of rubber hydrocarbon.

It is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. The process of vulcanizing a diene polymer rubber which comprises incorporating therein sulfur and an accelerating amount of a compound of the formula where T is selected from the group consisting of benzothiazolyl, nitro-, chloro-, lower alkyl-, and lower alkoxy-substituted benzothiazolyl, and x is an integer at least 5 but less than 7 and heated at a vulcanizing temperature.

2. The process of claim 1 where T is benzothiazolyl andxis 5.

3. The process of claim 1 where T is benzothiazolyl and x is 6.

References Cited UNITED STATES PATENTS 5/1930 Teppema 260793 1/1940 Williams 260-793 

1. THE PROCESS OF VULCANIZING A DIENE POLYMER RUBBER WHICH COMPRISES INCORPORATING THEREIN SULFUR AND AS ACCELERATING AMOUNT OF A COMPOUND OF THE FORMULA 